The Tato Nano: $2500 and 50 mpg

What's the difference between this and a smart car? I saw one of those on the highway keeping up. I'd be afraid to drive something this light on the freeway, but it'd be fine for bopping around the neighborhood doing errands. It's better than my sister's Gemcar which has little storage, no doors, can't handle hills, and only goes 26 mph. The worst is the windchill factor.